Metal filaments suitable for textiles



April 23, 1968 H. H. WEBBER E AL ,3

METAL FILAMENTS SUITABLE FOR TEXTILES Original Filed March 14, 1965FIE-3.1 1r5.2F"1E1. a F154 II/Il HQ?" 1 15.12 27 Qlberifllfldsa m fmwvfimew 2595i United States Patent 3,379,000 METAL FILAMENTS SUITABLEFOR TEXTILES Harold H. Webber, Groton, Mass, and Albert H. Wilson, Jr.,De Land, Fla., assignors to Roehr Products Co., Inc., a corporation ofDelaware Application Mar. 14, 1963, Ser. No. 265,262, which is acontinuation of application Ser. No. 463,759, June 14, 1965, now PatentNo. 3,277,564, dated Oct. 11, 1966. Divided and this application Sept.15, 1965, Ser. No.

7 Claims. (Cl. 57-139 ABSTRACT OF THE DISCLOSURE This applicationcomprises a divisional of application Ser. No. 463,759 filed June 14,1965, now US. Patent No. 3,277,564, comprising a continuation ofapplication Ser. No. 265,262 filed Mar. 14, 1963, now abandoned.

This invention relates to the forming of filamentsand in particular tothe forming of fine filaments having a diameter of approximately micronsor below.

There has long been a need for high strength metallic filaments and thelike for use in fabrics having improved physical characteristics ascompared to the conventional textile fabrics such as cotton, wool andthe like. One example of such a need is that of the automative vehicletire industry wherein reinforcing fabrics of many different types havebeen employed over the years in an attempt to find a completelysatisfactory carcass reinforcing fabric.

F-urther, recent investigations of the tensile strength of smalldiameter metal filaments such as whiskers of iron, copper, silver andthe like having a diameter of under microns have indicated thatfilaments of this type having a diameter of approximately 4 microns orless have increased tensile strength substantially beyond the expectedtensile strength as determined by Hookes law. Thus the desirability offorming such small diameter filaments in substantial quantities and .arelatively low cost is manifest. The present invention comprehends animproved process for producing such filaments at such low cost and thusmakes available for the first time commercially practical high strengthfilaments of metal and the like for use in improved fabrics, cables,filter media, superconductive bodies, etc.

A principal feature of the invention is the provision of a new improvedfilament product.

A further feature of the invention is the provision of a tow offilaments having a diameter of approximately 10 microns and below and insubstantially continuous lengths such as in lengths of approximately 50feet and over.

Still another feature of the invention is the provision of suchfilaments having controlled uniformity.

Yet another feature of the invention is the provision of such a towcomprising unburnished metal yarn.

Still another feature of the invention is the provision of such a towwherein the filaments are formed in a novel twisted relationship.

Other feaures and advantages of the invention will be ice apparentfrom'the following description taken in connection with the accompanyingdrawing:

FIG. 1 is a transverse cross-section of a metal wire from which a tow offilaments may be formed in accordance with the invention;

FIG. 2 is a transverse cross-section of the wire disposed within acoaxial sheath as in a first step of the method of forming thereof;

FIG. 3 is a transverse cross-section of the wire and sheath assemblywith the sheath reduced in diameter as in a subsequent step;

FIG. 4 is a transverse cross-section of the sheathed wire structure asreduced in diameter in a further subsequent step;

FIG. 5 is a transverse cross-section of a plurality of sheathed wirestructure of FIG. 4 arranged within a further sheath to define a bundle;

FIG. 6 is a transverse cross-section of the bundle of FIG. 5 as reducedin diameter in a subsequent step;

FIG. 7 is a transverse cross-section of a plurality of thereduced-diameter bundles of FIG. 6 disposed in a further sheath todefine a bundle of said bundles;

FIG. 8 is a transverse cross-section of the bundle of FIG. 7 as reducedin diameter in a subsequent step;

FIG. 9 is a transverse cross-section of a plurality of the reduceddiameter bundles of FIG. 8 disposed in a further sheath to define abundle of said bundles;

FIG. 10 is a transverse cross-section of the bundle of FIG. 9 reduced indiameter in a subsequent step;

FIG. 11 is a fragmentary diagrammatic vertical section of an apparatusfor drawing the filaments in practicing the method embodying theinvention;

FIG. 12 is a vertical cross-section of a tank wherein the reduceddiameter bundle of FIG. 10 is disposed to be acted upon by a suitablefluid within the tank to remove the sheath material from the bundle; and

FIG. 13 is a tow of filaments embodying the invention.

In the exemplary embodiment of the invention as disclosed in thedrawing, a tow generally designated 10 of filaments 11 is formed by aprocess wherein a plurality of relatively large diameter wires 13 areconstricted or otherwise reduced in diameter in a bundle arrangement soas to result in the individual filaments 11 being of extremely smalldiameter while yet of substantial length. More specifically, theinvention comprehends the forming of metal filaments and the like havinga diameter of approximately 10 microns more or less and down to under 1micron if desired. Thus, the invention may be employed in the formationof fine filaments including whisker-type filaments wherein substantiallysingle crystal diameters are provided. Further, the inventioncomprehends the provision of such fine filaments in substantiallengthssuch as approximately 50 feet and over whereas heretofore whiskers havebeen limited to relatively short lengths due to the presence of fracturepoints and the like occurring in the knwon methods of formation thereof.

The present invention comprehends the forming of such fine filaments byconstriction of a plurality of wires and more specifically by successivedrawing operations. In the illustrated embodiment a wire 13 having arelatively large diameter such as over .05 inch is firstly encased in asheath 14 of suitable matrix material. As shown in FIG. 2, the sheathmay have an internal diameter slightly larger than the external diameterof the wire 13 to permit facilitated coaxial assembly thereof. Asindicated briefly above, the filaments 11 may comprise metal filaments.Examples of material of which the wire 13, and thus the filaments 11 maybe formed by the present process, comprise niobium, stainless steel,nickel, tungsten, iron, aluminum, carbon steel, and chrome nickelalloys, and other suitable drawable materials. The wire 13 may besuitably formed to have an originally small diameter by any suitablemethod including melt forming, foil slitting, electrodeposition, vaporphase deposition, chemical deposition, powder forging, and suitableconventional wire forming processes. It is preferable that the wire 13be relatively free of occlusions and the like to preclude formation offracture points in the wire in the drawing process. The wire may haveany suitable cross-section including the circular cross-sectionillustrated in FIG. 1. Further, the wire may be longitudinally uniformin cross-section or may vary as desired.

The sheath 14 may be formed of a suitable matrix material which will actgenerally as a fluid medium under the pressures induced at the localityof that drawing dies. Examples of such matrix material are metals suchas copper and iron.

As shown in FIG. 3, the sheath 14 is firstly constricted onto the wire13 to make a tight physical bond between the sheath and the wire so thatin subsequent drawing steps the sheath 14 remains fixed relative to thewire 13 and does not stretch thereover. The assembly 15 of the wire 13and thusly reduced sheath 14 is next drawn down through a suitable diesuch as die 16 illustrated in FIG. 11. The assembly 15 is forced throughthe die by suitable pulling means diagrammatically illustrated at 17 inFIG. 11. The resultant reduced-diameter sheathed wire generallydesignated 18 is illustrated in FIG. 4.

A plurality of sheathed wires 18 are next disposed within a sheath 19formed of a suitable matrix material which may, but need notnecessarily, comprise the same material as sheath 14. As shown in FIG.5, the sheathed wires 18 may be uniformly distributed within the sheath19 where it is desired to obtain filaments 11 of generally uniformcross-section.

The bundle 20 of sheathed wires 18 in sheath 19 is then drawn down todefine a reduced-diameter bundle generally designated 21 as shown inFIG. 6. The plurality of the reduced diameter bundles 21 may then bedisposed within a further sheath 22 as shown in FIG. 7 to define afurther bundle generally designated 23. The bundle 23 may then be drawndown to define a reduceddiameter bundle generally designated 24 as shownin FIG. 8. A plurality of the reduced-diameter bundles 24 may then bedisposed within a further sheath 25 as shown in FIG. 9 to define afurther bundle generally designated 26. The bundle 26 may then be drawndown, as shown in FIG. 10, to define a final reduced-diameter bundlegenerally designated 27.

The number of wires and bundles disposed within the bundling sheaths andthe number of drawing steps may be varied as desired to obtain thedesired resultant filament diameter; for facilitated illustration ofinvention we have shown three bundling and subsequent drawing steps withseven sheathed wires and bundles being disposed within the respectivebundling sheaths, it being understood that more or less Wires, bundles,and steps may be employed as desired.

The individual filaments 11 are obtained from the final bundle 27 byremoving the matrix material which comprises the various sheathsemployed in the drawing operation. As illustrated in the drawing, therespective constricting operations effected by the drawing steps causethe sheath material to substantially completely fill the voids betweenthe wires so as to form a matrix extending substantially continuously incross-section whereby each of the wires in the respective bundles isfirmly and positively supported by the matrix material during thedrawing thereof through the drawing die 16. As indicated briefly above,the matrix material preferably comprises a material capable of acting inthe manner of a fluid under the pressure induced at the drawing die soas to provide improved support of the wires during the drawing operationand thereby effectively preclude the formation of discontinuities in therespective wires.

The respective filaments 11 are subsequently made to comprise a filamenttow by the removal of the matrix material in a subsequent step of theforming process. The present invention comprehends the removal of thematrix material by suitably acting on the final bundle 27 to eliminatethe matrix material while allowing the filaments to remain. Thus, theinvention comprehends the use of a matrix material which differs inphysical characteristics from the wire material from which the filamentsare formed in such a manner as to permit the ready removal of the matrixmaterial without substantially affecting the filaments. For thispurpose, the sheath-matrix material may comprise, as indicated above,copper where the filament material is stainless steel permitting thecopper to be removed by treatment with suitable copper-dissolving acid,such as nitric acid, which leaves the stainless steel filamentssubstantially unaffected. Other methods of removal of the matrix may beemployed with suitable matrix materials permitting the removal thereofsuch as by electrolysis, shock, melting, physical break-up as bychopping and the like.

In the illustrative example of matrix removal step, as shown in FIG. 12,the bundle 27 is disposed in a suitable tank 28 containing a body 29 ofsolubilizing fluid such as nitric acid, the matrix material of bundle 27illustrated therein being copper and the filaments being stainlesssteel. Thus upon complete removal of the copper matrix material, theindividual filaments 11 define a tow 10 of stainless steel filaments asshown in FIG. 13, each filament being separate of the other filamentsand of preselected small diameter.

Specific examples of filament forming processes embodying the inventionare as follows:

Example 1.-A wire 13 of type 302 hard drawn stainless steel having adiameter of .081 inch is inserted into a copper tube sheath 14 having a.125 inch outer diameter and a wall thickness of .020 inch. In the firststep the sheath is drawn down to an outer diameter of .109 inch. Theresultant sheathed wire 18 is then annealed at a temperature ofapproximately 1800 F. The reduced sheathed wire 18 is then subsequentlydrawn seriatim in a number of similar drawing and annealing steps untilthe final outer diameter of the sheath wire 18 is approximately .016inch.

The .016 inch diameter sheathed wire 18 is then cut into 19 pieces andinserted into a copper sheath 19 having an outer diameter ofapproximately .125 inch and a wall thickness of approximately .015 inch.The sheath is then drawn down to an outer diameter of .109 inch and theassembly annealed at approximately 1800 F. The resultant bundle 20 isthen drawn down in suecesive steps including interposed annealing stepsto an ultimate diameter of .016 inch. The resultant reduced-diameterbundle 24 is then cut into 19 pieces and inserted in a copper sheath 26similar to sheath 19. The above steps are then repeated to again reducethe bundle to a final diameter of .040 inch wherein the individual wireshave been reduced in diameter to define filaments having a diameter ofapproximately .0005 inch. Alternatively, the final draw may be to adiameter of .032 inch to produce filaments of approximately .0004 inchdiameter, or to a diameter of .028 inch to produce filaments ofapproximately .00032 inch (8 microns) diameter. The matrix coppermaterial is then dissolved in tank 28 with the nitric acid 29 beingmaintained at a temperature of approximately F.

Example 2.-A stainless steel wire 13 having a diameter of .083 inch isinserted into a copper tube sheath 14 having a .125 inch outer diameterand a wall thickness of .020 inch. In the first step the sheath is drawndown to an outer diameter of .109 inch. The resultant sheathed wire 18is then annealed at a temperature of approximately 1800 F. The reducedsheathed wire 18 is then subsequently drawn seriatim in a number ofsimilar drawing and annealing steps until the final outer diameter ofthe sheathed wire 18 is approximately .016 inch.

The .016 inch diameter sheathed wire 18 is then cut into 7 pieces andinserted into a copper sheath 19 having an outer diameter ofapproximately .072 inch and a wall thickness of approximately .009 inch.The sheath is then drawn down to an outer diameter of .065 inch and theassembly is annealed at approximately 1800 F. The resultant bundle 20 isthen drawn down in successive steps, including interposed annealingsteps, to an ultimate diameter of .016 inch. The resultantreduced-diameter bundle 24 is then cut into 7 pieces and inserted in asuitable copper sheath '26 similar to sheath 19. The above steps arethen repeated to reduce the bundle to a final diameter of .016 inchwherein the individual wires have been reduced in diameter to definefilaments having a diameter of approximately ,00032 inch. Alternatively,the final draw may be to a diameter of .032 inch to produce filaments ofapproximately .00047 inch diameter, or to a diameter of .025 irich toproduce filaments of approximately .0004 inch (10 microns) diameter. Thematrix copper material isthen dissolved in tank 28 with the nitric acid29 being maintained at a temperature of approximately 120 F.

Example 3.--A wire 13 of type 302 hard drawn stainless steel wire havinga diameter of .083 inch is inserted into a copper tube sheath 14 havinga .125 inch outer diameter and a wall thickness of .020 inch. In thefirst step the sheath is drawn down to an outer diameter of .109 inch;The resultantsheathed wire 18 is then annealed at a temperature ofapproximately 1800 F. 'The reduced sheathed wire 18 is then subsequentlydrawn seriatim in a number of similar drawing and annealing steps untilthe final outer diameter of the sheathed wire 18 is approximately .025inch.

The .025 inch diameter sheathed wire 18 is then cut into 37 pieces andinserted into a copper sheath 19 having an outer diameter ofapproximately .250 inch and a wall thickness of approximately .030 inch.The sheath is then drawn down to an outer diameter of .225 inch and theassembly is annealed at approximately 1800 F. The re sultant bundle 20is then drawn down in successive steps, including interposed annealingsteps, to an ultimate diameter of .025 inch. The resultant reduceddiameter bundle 24 is then cut into 37 pieces and inserted in a suitablecopper sheath 26 similar to sheath 19. The above steps are then repeatedto reduce the bundle to a final diameter of .049 inch wherein theindividual wires have been reduced in diameter to define filamentshaving a diameter of approximately .0005 inch. Alternatively the finaldraw may be to a diameter of .035 inch to produce filaments ofapproximately .004 inch diameter, or to a diameter of .028 inch toproduce filaments of approximately .0003 inch (7 /2 microns) diameter.The matrix copper material is then dissolved in tank 28 with the nitricacid 29 being maintained at a temperature of approximately 120" F.

Example 4.--A wire 13 of alloy 270 soft nickel having a diameter of .063inch is inserted intoa copper tube sheath 14 having a .095 inch outerdiameter and a wall thickness of .015 inch. The sheathed wire is drawnseriatim in a number of drawing and annealing steps until the finalouter diameter of the sheathed wire 18 is approximately .016 inch.

The .016 inch diameter sheathed wire is then cut into 19 pieces andinserted into a copper sheath 19 having an outer diameter ofapproximately .125 inch and a wall thickness of approximately .015 inch.The bundle 20 is drawn down in successive steps to an ultimate diameterof .018 inch. The reduced diameter bundle is then cut into 19 pieces andinserted in a suitable copper sheath 26 similar to sheath 19. The abovesteps are then repeated to again reduce the bundle to a final diameterof .028 inch wherein the individual wires have been reduced in diameterto define filaments having a diameter of approximately .0004 inch (10microns). The matrix copper material is then dissolved in tank 28 withthe nitric acid 29 being maintained at a temperature of approximately120 F.

Example 5.Awire of type 304 hard drawn stainless steel having a diameterof .062 inch is inserted into a copper tube sheath 14 having a .095 inchouter diameter and a wall thickness of .015 inch. The sheathed wire 18is then subsequently drawn seriatim in a number of similar drawing andannealing steps until the final outer diameter of the sheathed wire 18is approximately .016 inch.

The .016 inch diameter sheathed wire 18 is then cut into 19 pieces andinserted into a copper sheath 19 having an Outer diameter ofapproximately .125 inch and a wall thickness of approximately .015 inch.The sheath is then drawn down. to an outer diameter of ,109 inch and theassembly is annealed at approximately 1800 F. The resultant bundle 20 isthen drawn down in successive steps, including interposed annealingsteps, to an ultimate diameter of .016 inch. The resultantreduced-diameter bundle 24 is then cut into 19 pieces and inserted in asuitable copper sheath 26 similar to sheath 19. The above steps are thenrepeated to reduce the bundle to a diameter of .028 inch. The reducedbundle is then cut into 7 pieces and inserted into a copper sheathhaving an outer diameter of inch and a wall thickness of .015 inch. Thebundle is then drawn down by successive steps to a diameter of. 0.16inch. This reduced-diameter bundle is then cut into 19 pieces andinserted into a copper sheath having an outer diameter of .125 inch anda wall thickness of .015 inch. This bundle is then drawn down bysuccessive steps to a final diameter of .032 inch wherein the filaments11 have a diameter of approximately .00010 to .000 12 inch (2 /2 to 3microns).

Example 6.A wire 13 of type 304 stainless steel having a diameter of.062 inch is inserted into a low carbon steel tubular sheath 14 havingan outer diameter of .125 inch and a wall thickness of .023 inch. Thesheathed wire is drawn seriatim in a number of drawing and annealingsteps until the final outer diameter thereof is approximately .020 inch.

The .020 inch sheathed wire 18 is then cut into 19 pieces and insertedinto a low carbon steel sheath 19 having an outer diameter ofapproximately 1.56 inches and a wall thickness of approximately .023inch. The bundle 20 is drawn down in successive steps to an ultimatediameter of .020 inch. The reduced-diameter bundle is then cut into 19pieces and inserted into a copper sheath 26 similar to sheath 19. Theabove steps are then repeated to reduce the bundle to a final diameterof .025 inch wherein the individual filaments have a diameter ofapproximately .0004 inch (10 microns).

The resultant filaments 11 by virtue of their extremely small diametershave textile characteristics in that they are highly compliant (i.e.they will bend around their own diameter without a permanent set), areflexible, and may be used in conventional textile machinery for formingfabrics and-the like. The filaments may be formed in sub stantiallengths such as over 50 feet. Such continuous filaments are highlydesirable in fabric formation as compared to the short stable fibersobtainable in other filament forming processes such as cold and hotdrawing, cold and hot swaging, cold and hot rolling, and cold and hotextrusion processes,

The tows 10 may be provided with the individual filaments 11 thereinhaving a preselected twist by suitably twisting the bundles during thedrawing steps. By suitably annealing the twisted drawn bundle, thetwisted arrangement of the filament may be permanently set therein.Thus, by suitably twisting the individual bundles of the multiplebundles 23 and 26 substantially complete elimination of twisting forces'in the composite multiple bundle may be obtained. Still further, byproviding the wires 13 with varying diameter in the longitudinaldirection, the resultant filaments may correspondingly have varyingdiameters along their longitudinal extent as desired. As the resistivityof the wires is a function of the cross-section diameter of the wirescontrolled resistivity may be obtained. As the wires 13 are twistedabout the longitudinal axis of the bundle, the resultant filaments areformed in spaced concentric helices wherein the matrix materialmaintains the spacing thereof until removed in the leaching step.

As indicated briefiy above, the inventive concept comprehends a limitingof the constriction of the filaments to have at least one crystalthickness to provide improved high strength filaments.

While we have shown and described certain embodiments of our invention,it is to be understood that it is capable of many modifications.Changes, therefore, in the construction and arrangement may be madewithout departing from the spirit and scope of the invention as definedin the appended claims.

We claim:

1. A tow of metal filaments each having a maximum cross-section of lessthan approximately 10 microns and a length of greater than approximately50 feet and having a trace amount of a different material diffused inthe outer surface thereof.

2. The tow of filaments of claim 1 wherein the filaments aresubstantially free of surface burnishing,

3. The tow of filaments of claim 1 wherein the filaments are ofsubstantially one crystal thickness throughout the length thereof.

4. A tow of filaments as set forth in claim 1 wherein the filaments aresubstantially identically cold worked at each transverse cross-sectionof the tow.

5. A tow of filaments as set forth in claim 1 wherein the filaments havea substantially uniform total crosssectional area in different planestaken at positions spaced axially along the tow.

6. A tow of filaments as set forth in claim 1 wherein the filaments areformed in spaced concentric helices.

7. The tow of metal filaments of claim 1 wherein said different materialcomprises a metallic material.

References Cited UNITED STATES PATENTS 1,012,031 12/1911 Underwood139-425 1,096,077 5/1914 Underwood.

2,050,298 8/1936 Everett 29-423 X 2,077,682 4/1937 Everett 29-4192,532,395 12/1950 Dreyfus 57-140 2,570,748 10/1951 Bain et al. 29-4242,825,108 3/1958 Pond 29-143 3,090,189 5/1963 Boussu et al. 57-1393,090,190 5/1963 Boussu et al 57-139 JOHN PETRAKES, Primary Examiner.

